The present project is an outgrowth of our long-range research program concerned with the elucidation of neuroendocrine phenomena on a comparative basis. Our experimental invertebrate model of choice is the insect Leucophaea maderae. Initially having been focused on the special status of neurohormone-producing neurosecretory cells, the study now includes the analysis of a growing number of additional peptidergic neurons. Their immunocytochemical characterization by use of polyclonal antibodies is still in progress. The main objective of the present program is to carry the search for chemical specificity further by screening tests with monoclonal antibodies addressing the entire spectrum of neurotypes existing in this insect. The rationale for the intended use of monoclonal antibodies raised against mammalian antigens is twofold: (a) The information available from tests with this new class of markers on the remarkable chemical individuality in the nervous system of vertebrates will provide guidelines for the chemical characterization of the insect neurons under investigation. (b) Reactivity of neural structures of insects with mammalian monoclonal antibodies may provide us with additional and principally significant insights regarding the evolutionary history of neurotypes and neuron-specific molecules, and the evolvement of heterogeneous organelles such as neurofilaments.